Dynamic Image as Section Background

I am trying to have an image from the content library on my project page to appear as a background of the first section of the page.
I tried to add a dynamic image in the section to show full screen in all instances but it doesn’t work well, since there is always a margin that appear on left, right or bottom when resizing. So I thought a background image would solve the issue. but I don’t see a way to link the background image to the library of assets.

hmmm, I’m not 100% sure here, if this will be achievable without code, but still I got some questions:
since this is the image from content library, image got to change to another one on some specific circumstance? or it is dynamic pages, so once you are visiting another page, the background got to change?
can not promise if solution will be found, but still more details along with some video example could make investigation easier

this is for a dynamic page of a collection of projects. Just have the main image (hero image of a dynamic single page) to be like a section background image, which would mean being able to link the background image of the section to the project image in the dataset

With Velo:
If you are using a section you can’t:
image

If you are using a flexbox you can’t:
image

I can’t find an easy guide into which elements have access to background-image.